which is why I came to the conclusion that a voltage spike must have damaged something,
No components of that sort of age can suffer random failures nothing needs to have damaged it. It is rare that a faulty component can be identified just by looking at it. When you can, it is when it has suffered a catastrophic failure, either from external excess or damage that has occurred once it has failed and no longer is serving it's function.
Capacitors can also go but it is a bit more difficult to measure them in circuit.
Have you got any test equipment? A good scope is almost essential.